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    <title>Document</title>
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    <script>
        
        // let a = "凯哥";
        // a.index = 20;
        // console.log(a.index);   //undefined


        // let b = {};
        // b.index = 10;
        // console.log(b);


        let a = new String("凯哥");
        console.log(a + "朱雀");

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